U.S. Pat. No. 3,334,259 issued to T. M. Shrader on Aug. 1, 1967 discloses a color selection electrode, or shadow mask, having a plurality of strap-like support springs, usually four, attached to a frame which supports the mask. The mask-frame assembly is positioned within a faceplate panel and is spaced therefrom using a suitable spacer device. The support springs are depressed toward the mask frame and flat washers are inserted over support studs embedded into the interior wall of the faceplate. The washers are located between the support springs and the studs and at this point in the manufacturing process the washers are free to move, relative to the support springs, to facilitate obtaining the precisely desired distance, called the Q-spacing, between the mask and the faceplate and a precise alignment of the stud-receiving apertures of the washers with the support studs. The washers are then attached to the support springs using temporary tack welds. Then, with the completely assembled mask assembly removed from the panel, a more secure weld using larger equipment is provided. The reason for making the initial tack weld is that larger welding equipment cannot easily be fitted into the space between the mask frame and the faceplate panel sidewall when the mask assembly is disposed within the panel. A drawback of the patented structure is that the tack weld tends to be relatively weak and often breaks when the mask assembly is removed from the panel. Additionally, the insertion and removal process for final welding is inefficient and adds to the assembly cost of the tube.
In order to improve manufacturing efficiency, it is now usual for the studs to be affixed at a controlled height above the surface of the panel to obtain the desired Q-spacing. Four studs are usually provided, one near the midpoint of the upper long side of the sidewall, one near the midpoint of each of the short sides of the sidewall, and one displaced slightly from the midpoint of the lower long side so that the mask cannot be inserted incorrectly. The support springs attached to the upper long side and the short sides of the mask now include stud-engaging apertures in their distal end; however, the support spring that engages the stud located on the lower long side of the panel continues to use a washer disposed between the distal end of the spring and the stud to provide a manufacturing tolerance to compensate for manufacturing variations or tolerances in stud placement and spring location.
U.S. Pat. No. 4,467,242 issued to L. P. Wilbur, Jr., et al. on Aug. 21, 1984 discloses an off-set washer which provides additional compression of the support spring to which the washer is attached. The height of the off-set can be adjusted to provide sufficient space between the mask frame and the faceplate panel sidewall to permit the washer to be permanently welded to the distal end of the support spring.
It is known that electrical resistance welding frequently produces weld splash, or weld-generated debris, consisting of metal particles of the joined parts. This weld splash is initially molten and thus usually adheres to the surface on which it lands. To minimize weld-splash, which can become dislodged to create particles within the tube, it is known to shield the adjacent sidewall of the faceplate with a mechanical device, such as a plastic strip, which functions as a protective shield. Such a shield, however, infringes on the available welding space and must be accurately located if it is to function properly. An improperly located shield, in addition to being ineffective in preventing weld splash from impinging on the sidewall of the faceplate panel, can also interfere with the welding electrode, causing improper washer-to-support spring welds.